Microfluidic valve with partially restrained element

ABSTRACT

The invention provides microfluidic devices having valves disposed therein. The valves can be configured as one-way valves. The invention also provides microfluidic pumps using two or more microfluidic valves. The valves can be configured to rest in an open or closed position. The valves also can be single use valves or can be multiple use valves. The valves may be further responsive to actuators, including electromechanical and magnetic actuators.

FIELD OF THE INVENTION

[0001] The present invention relates to microfluidic devices havingvalves therein. The invention also relates to microfluidic pumps.

BACKGROUND

[0002] Microfluidic devices are becoming more important in a variety offields, from biochemical analysis to medical diagnostics and to fieldsas diverse as environmental monitoring to chemical synthesis. There hasbeen a growing interest in the manufacture and use of microfluidicsystems for the acquisition of chemical and biological information. Inparticular, microfluidic systems allow complicated biochemical reactionsto be carried out using very small volumes of liquid. These miniaturizedsystems increase the response time of the reactions, minimize samplevolume, and lower reagent cost.

[0003] Traditionally, these microfluidic systems have been constructedin a planar fashion using silicon fabrication techniques. Representativesystems are described, for example, in some early work by Manz et al.(Trends in Anal. Chem. (1990) 10(5): 144-149; Advances in Chromatography(1993) 33: 1-66). These publications describe microfluidic devicesconstructed using photolithography to define channels on silicon orglass substrates and etching techniques to remove material from thesubstrate to form the channels. A cover plate is bonded to the top ofthis device to provide closure.

[0004] More recently, a number of methods have been developed that allowmicrofluidic devices to be constructed from plastic, silicone or otherpolymeric materials. In one such method, a negative mold is firstconstructed, and plastic or silicone is then poured into or over themold. The mold can be constructed using a silicon wafer (see, e.g.,Duffy et al., Analytical Chemistry (1998) 70: 4974-4984; McCormick etal., Analytical Chemistry (1997) 69: 2626-2630), or by building atraditional injection molding cavity for plastic devices. Some moldingfacilities have developed techniques to construct extremely small molds.Components constructed using a LIGA technique have been developed (see,e.g., Schomburg et al., Journal of Micromechanical Microengineering(1994) 4: 186-191). Other approaches combine LIGA and a hotembossingtechnique. Imprinting methods in polymethylmethacrylate (PMMA) have alsobeen demonstrated (see, Martynova et al., Analytical Chemistry (1997)69: 4783-4789). However, these techniques do not lend themselves torapid prototyping and manufacturing flexibility. Additionally, thesetechniques are limited to planar structures. Moreover, the tool-up costsfor both of these techniques are quite high and can be cost-prohibitive.

[0005] Generally, construction of microfluidic devices having integralpumps and valves is problematic using the traditional techniques ofmicrofluidic device construction. Rigid silicon fabrication, forexample, does not lend itself to construction of flexible parts. Oftendevices containing integrated valves and pumps are complex and difficultto manufacture. Such devices also can require several differentmanufacturing techniques to create the valve or pump structures. Inspite of the limitations in the current state of the art, there is aclear need in the field of microfluidic devices for improved valves andpumps.

SUMMARY OF THE INVENTION

[0006] This invention relates to the microfluidic devices that containvalves for controlling fluid flow. In one aspect of the presentinvention, certain sections of microfluidic channels are partiallyrestrained, that is, not connected at all points. Since certain sectionsare not completely held in place, the material in this area is flexibleand can form a microfluidic flap. These flaps can be used to control theflow of fluid. In certain embodiments, these flaps can be used asone-way flow controllers. In other embodiments, these flaps can be usedto pump fluids. In still further embodiments, these flaps can be used todirect fluid among different levels of a three-dimensional device.

[0007] The invention provides a microfluidic valve device having a firstmicrofluidic channel disposed in a first layer. The microfluidic devicehas a second microfluidic channel in a second layer with at least onedimension smaller than that of the first channel. The device has a(third) flap layer disposed between the first microfluidic channel andthe second microfluidic channel, the third layer having a movable flapformed therein. The flap has a closed position sealed against a sealingsurface formed by the second layer and can open into the firstmicrofluidic channel. The flap can have at least one dimension,typically width, that is smaller than that of the channel into which itis deflected.

[0008] The flap can be formed from a material that is flexible orsubstantially rigid. When the flap is substantially rigid, the flap canhave a hinge region. The hinge region can be a portion of the materialthat has a reduced thickness relative to the movable portion of theflap. In another embodiment, the hinge region is constructed from adifferent material from the movable portion of the flap.

[0009] The layers of the device can be integral in the device or can beassembled from individual stencil layers. The stencil layers can be anysuitable material including polymeric materials. The stencil layers canbe, for example, adhesive tapes.

[0010] The device can be constructed such that the movable flap cancontact one or more surfaces of the first channel, and restrict fluidflow therein. The microfluidic device also can have a sealing layeradjacent to the flap layer with holes or apertures disposed therein toallow fluid communication through the flap region. The sealing layer canbe a substantially rigid material. The sealing layer also can contain anaperture disposed adjacent to the movable flap.

[0011] The movable flap can be flexible, substantially rigid, or acombination of flexible and rigid portions. When the movable flap issubstantially rigid, it can have a hinge region. A hinge region can beformed from a flexible material. Either the top or bottom or bothsurfaces of the movable flap can be adhesively coated.

[0012] The invention also provides microfluidic pumps that have two ormore microfluidic valves of the invention arranged in fluidcommunication with a pumping chamber having an adjustable volume. Thepumping chamber can be, for example, a cylinder with a movable pistonfor changing the volume. The pumping chamber also can have a deformablemembrane forming one surface of the pumping chamber. The deformablemembrane can be deformed to change the volume of the pumping chamber.Deformation can be achieved with a mechanical actuator including, forexample, an electromechanical actuator. Electromechanical actuatorsinclude, for example, piezoelectric materials. The pumping device alsocan have a pressurizable chamber that has at least one side formed bythe deformable membrane. The pressure in the pressurizable chamber canbe adjusted, for example, using a pump. Such a pressure change can causethe membrane to be deformed and thereby operate the pump.

[0013] Definitions

[0014] The term “channel” as used herein is to be interpreted in a broadsense. Thus, it is not intended to be restricted to elongatedconfigurations where the transverse or longitudinal dimension greatlyexceeds the diameter or cross-sectional dimension. Rather, such termsare meant to comprise cavities or tunnels of any desired shape orconfiguration through which liquids may be directed. Such a fluid cavitymay, for example, comprise a flow-through cell where fluid is to becontinually passed or, alternatively, a chamber for holding a specified,discrete amount of fluid for a specified period of time. “Channels” maybe filled or may contain internal structures comprising valves orequivalent components.

[0015] The term “microfluidic” as used herein is to be understood,without any restriction thereto, to refer to structures or devicesthrough which fluid(s) are capable of being passed or directed, whereinone or more of the dimensions is less than 500 microns.

[0016] The term “microfluidic flap” as used herein is to be understood,without any restriction thereto, to refer to a portion of a surfaceforming a wall of a microfluidic channel that is not connected at allpoints to other portions of the structure forming the channel. Amicrofluidic flap can have the property that it may move within saidchannel when certain physical characteristics of the channel change,such as pressure, temperature, flow rate of fluid, type of fluid, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1A shows an exploded view of a microfluidic device having amicrofluidic valve disposed therein. FIG. 1B shows a top view of thesame device assembled. FIG. 1C shows a side view of the device duringoperation. The dark arrow shows the direction of fluid flow. FIG. 1Dshows the same side view of the device during operation with the flowreversed. Again, dark arrows indicate the direction of fluid flow withinthe device.

[0018]FIG. 2A shows an exploded view of a microfluidic device capable ofbeing used to pump fluid. FIG. 2B shows a top view of the device of FIG.2A. FIGS. 2C and 2D show cross-sectional views of the same device inoperation. FIG. 2C shows the device with a negative pressure applied tochamber 111, while FIG. 2D shows the device with a positive pressureapplied to chamber 111.

[0019]FIGS. 3A and 3B show cross-sectional views of a microfluidicdevice having a microfluidic diversion valve therein where the flapportion is usually in the down position. In FIG. 3A, the device is showin operation with fluid flowing according to the single arrows throughchannels 189 and 192. In FIG. 3B, fluid is flowing in the reversedirection through channels 191 and 189 as indicated by the singlearrows. In both cases, fluid flows through filter region 190.

[0020]FIGS. 3C and 3D show cross-sectional views of a microfluidicdevice having a microfluidic diversion valve therein where the microflapportion is usually in the up position. In FIG. 3C, the device is show inoperation with fluid flowing according to the single arrows throughchannels 192 and 189. In FIG. 3D, fluid is flowing in the reversedirection through channels 191 and 189 as indicated by the singlearrows. In both cases, fluid flows through filter region 190.

[0021]FIG. 4A shows a top view of a microfluidic device having a flapvalve therein. FIG. 4B shows the same device with the flap deformedtowards channel 220 while FIG. 4C shows the same device with the flap inthe closed position.

[0022]FIG. 5A shows a side view of a microfluidic device having a flapvalve therein, the device subject to no external forces. FIG. 5B shows aside view of the device of FIG. 5A, subject to application of anexternal force that deforms the flap valve upward. FIG. 5C shows a sideview of the same flap valve, subject to application of an external forcethat deforms the flap valve downward.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The invention provides microfluidic devices having fluid controlvalves disposed therein. In one embodiment, the valve is a one-way valveor a check valve. The microfluidic valve includes a first channel formedwithin a first layer of a microfluidic device and a second channelformed within a second layer of the microfluidic device substantiallycoplanar with the first channel. A layer disposed between the first andsecond layers forms a flap structure. The first channel is smaller thanthe second channel in at least one dimension within the plane of thechannels such that a seating surface is formed. A third layer disposedbetween the first and second layers has a flap that is movable withinthe device but remains attached to the third layer. In a preferredembodiment, the flap and the third layer are formed from the samematerial, with material removed from the third layer to form the flap.

[0024] The flap is movable, such that in a closed position it seals withthe seating surface. As used herein, the term “seals” refers to contactof a flap against a seating surface. Sealing of a flap includes both theformation of a fluid-tight junction and junction that allow restrictedfluid flow through the device. Mobility of the flap can be achieved byany suitable modification of the flap material or dimensions, including,for example, altering the material of the flap, the dimensions of theflap (e.g., thickness), the degree of connection of the flap to thethird layer and combinations thereof. For example, the flap can beformed from a substantially rigid material, with a hinge region to allowmovement. A hinge region can be formed in a rigid material by reducingits thickness at the desired hinge region. The flap also can be formedfrom a pliable material. A material is suitably pliable if, at thedesired operating pressures of the device, the material will bend ordeform. The degree of pliability will depend on the nature of thematerial used and on the thickness of the material used. A flap can haveany shape such that the flap can deform within the device towards thesecond channel. In certain embodiments, the flap will seal against thefirst channel within normal operating pressures of the device. In otherembodiments, the flap will seal against the second channel within normaloperating pressure of the device. In one embodiment, a flap has one sideseparated from the membrane from which it is formed. In anotherembodiment, the flap is formed by cutting three sides of a rectangleinto the membrane material to form a flap with a substantiallyrectangular shape.

[0025] The stencil layer or membrane in which the flap resides, the flaplayer, can be made of any suitable material. A suitable material can bechosen by one of skill in the art, depending on the type of constructionused to make the microfluidic device. For repeated usage, it ispreferred that the material chosen has a degree of elasticity allowingit to rebound into the seated position. For example, the material can bea metal foil, paper or polymer or combinations or laminates thereof.When the device is to be constructed from layered stencil layers, andthe flap is integral with the flap layer, the flap and flap layer arepreferably fabricated from a polymeric material. Suitable polymericmaterials include, for example, polytetrafluorethylenes, polystyrenes,polypropylene, polyethylene, polyimides, polyacrylates, rubbers andsilicones. In certain embodiments, one or both sides of the flap regionmay be covered or coated with a material to enhance adhesion to theupper or lower channel surface. The adhesion materials can be permanentor reversible. In a preferred embodiment, adhesive materials are coatedonto the surface that is to make up the flap portion prior to theconstruction of the device.

[0026] Microfluidic coupling devices have stencil layers and substratelayers that define channels therein. Such devices can be constructedfrom discrete layers of material or can be fabricated as an integralunit. When a coupling device is constructed as an integral unit, layersrefer only to positions within a device rather than to individualcomponents. A microfluidic device can be constructed with stencillayers, using techniques described, for example, in co-pending U.S.patent application Ser. No. 09/453,029, incorporated herein by referencein its entirety. When the device is to be constructed by assemblingstencil layers with adhesive separating the layers or usingself-adhesive tape materials, the material forming the sealing surfaceand the side of the flap region interacting with the sealing surface areboth preferably non-adhesive. Alternatively, the area of the flapinteracting with the sealing surface and/or the seating surface can beadhesively coated, and the adhesive strength can be chosen to preventpermanently closing the valve. Any suitable adhesive can be used toassemble a device from stencil layers.

[0027] The material chosen for use as a valve is preferablysubstantially impermeable to the fluid to be used in the device. Adevice can, however, use a material that is permeable to a fluid. In oneembodiment, the flap layer is formed from a material that is impermeableto the fluid for which the device is designed, but may be permeable to agaseous fluid, such as air.

[0028] In a preferred embodiment, the flap region may be used to seal ahole or via that goes from one level of the device to another. Incertain embodiments, the flap portion may be more effective at blockingfluid flow if it covers a hole or via rather than a channel portion.

[0029] The height of the outlet channel also can be varied to change theoperation of the flap. A large flap relative to the height of the outletchannel will allow the flap to seal against the lower surface of thechannel into which the flap is deflected. For example, referring to FIG.1D, membrane 22 having flap 30 disposed therein opens into channel 26 inlayer 23. The thickness of layer 23 (the height of channel 26) and thelength of the flap 30 can be varied such that the deflected flap may ormay not come in contact with the lower surface of layer 24.

[0030] Referring to FIG. 1, a microfluidic device is constructed fromfive stencil layers 20-24 that have channels 25, 26, vias 27, andinlet/outlet ports 28, 29. Additionally, one section 30 of layer 22 iscut so that the region is still attached to the stencil layer but canmove freely. The resulting flap 31 is only partially restrained frommoving. The completed device is shown in FIG. 1B and the region wherethe flap 31 is in contact with the upper sealing surface of layer 21 isshown. A cross section of region 31 is blown up in FIGS. 1C and D. Twopossible uses are shown. In FIG. 1C, fluid is injected at the entry port29. The fluid passes through channel 26 until it reaches the flap valveregion 31. Here, the flap region 30 is pushed down against the sealingsurface of stencil layer 21. Thus, the flap region 30 prevents fluidflow from channel 26 into channel 25. In operation, the fluid may neverreach the region at flap 30, since the fluid will compress the airwithin channel 26 and build up pressure which may prevent the fluid fromflowing at all. In operation in the reverse direction, when fluid isinjected at port 28, it passes through the vias 27 and through channel25. When the fluid now encounters the flap portion 30, the flap is freeto be displaced upwards since the area above it is open channel 26. Thefluid passes through this region, into channel 26 and can exit throughport 29.

[0031] Also provided is a microfluidic pump having a first inletchannel, a first microfluidic one-way valve, with a first flap openinginto a chamber in fluid communication with the first inlet channel, andan outlet channel in fluid communication with the chamber through thesecond microfluidic check valve. The second one-way valve has a secondflap opening into the second channel. The volume of the pumping chambercan be altered. In one embodiment, the pumping chamber is a cylinderwith a piston assembly. In another embodiment, the pumping chamber has adeformable membrane forming one side of the chamber. Deformation of thedeformable membrane can result in movement of the deformable membrane.The deformable membrane can be moved by mechanical force. For example,the membrane can be deformed using a mechanical actuator. In oneembodiment, the mechanical actuator is a piston. In another embodiment,the mechanical actuator is an electromechanical material, for example, apiezoelectric device of a Ti—Ni device. In another embodiment, thematerial can be a magnetic material and a magnetic field can befluctuated to force the membrane up and down. In another embodiment, thematerial can be driven up and down using a camshaft that isasymmetrical. In another embodiment, force to deform the membrane issupplied by having an additional chamber opposite the pumping chamber,the pressure of which can be varied, for example, by a pressure pump ora vacuum pump. In another embodiment, the temperature of the chamber 111can be cycled up and down to force movement of the membrane.

[0032] Referring to FIG. 2A, a microfluidic pumping system wasconstructed from nine stencil layers 100-108 that had channels 109-111,through regions 112, inlet outlet holes 113,114 and a pressure entrance115 removed. Additionally, two flap regions 116,117 we partially cut instencil layer 103. The assembled device is shown in FIG. 2B. The crosssection of pumping area 118 is shown in FIGS. 2C and D. In use, thepumped worked as follows. Fluid was injected at port 114 and filled bothchannels 109 and 110 and chamber 119. An external pressure/vacuum sourcewas hooked up to the inlet port 115. When the external source applied aslight vacuum to channel 111, the stencil layer 106 flexes up towardsthe channel 111. This creates a slight negative pressure in chamber 119directly below the stencil 106. In order to adjust for this, flap 117 islifted up towards the negative pressure and fluid flows into chamber119. Flap 116 does not open since it is blocked by the lower surface ofstencil layer 104 above. Once the chamber equilibrates (or prior toequilibration), the pressure on the external source at 115 was reversed.Referring to FIG. 3D, the positive pressure within channel 111 causesthe stencil layer 106 to push down into the chamber, increasing thepressure. In order to adjust to the new pressure, flap 116 opens towardschannel 110 and pushes fluid into outlet channel 110. When the pressureat the inlet 115 oscillates up and down, a net fluid flow from channel109 to 110 occurs. This pumping mechanism can be used to push fluidthroughout additional channels within the microfluidic structure, or topush fluid off board. The pumping speed and amount can be altered in anumber of ways. The size of the pressure change at the input 115 as wellas the period of the oscillation can have an effect. The geometry andsize of the channels themselves can also alter the pumping parameters.For example, the size of the flaps will determine the amount of fluidtransferred per stroke. Alternatively, the size of the chamber justbelow the stencil layer 106 can also be altered to change theparameters. Likewise, the material used to construct deformable membrane106 will determine the change in volume of pumping chamber 119, as willthe composition of the fluid itself.

[0033] Fluid control valves of the invention also can be used to directfluid flow among layers of a microfluidic device. These valves can beincorporated into a system in such as way that a particular microfluidicdevice can perform a variety of functions depending on how the chip isused. Additionally, channels within a particular device can be used morethan once for different functions when using these valves.

[0034] Microfluidic devices of the invention also can have filtermaterials embedded within the channels. A filter is any material thatpartially blocks or selectively alters fluid flow within a channel. Afilter is typically a porous material. The material also can havesurface chemical properties that alter its interaction with variousfluids to be used in the device.

[0035] Two similar configurations of the present invention that performin two distinct manners are shown in FIGS. 3A-D. These figures are ofthe cross-section of a portion of a complete device having valvestructures. In this particular embodiment, the devices contain filtermaterial for performing ultra-filtration of biological or chemicalmolecules. Referring to FIG. 3A, a device is shown with an input channel189 for loading a biological sample. Fluid injected into channel 189from the left will encounter filter material 187. When fluid isinjected, it goes across the filter area at 190 and into the regionabove. In this application, the filter is chosen so the biologicaltargets within the sample of choice will become stuck at the lowersurface of the filter 187 at region 190. In certain embodiments, thefilter can be chosen so that large nucleic acid targets will be blockedat the entrance of the filter and other non-specific biomass willproceed. The stencil layer 182 in this device is composed of a flexiblematerial so that the flap valve 188 rests on the lower stencil surface184 in the normal position. Additionally, semi-permanent adhesivematerial is used on the lower surface of the flap portion 193 and/or theupper surface of the lower stencil 184. In the normal position, channel191 is blocked and the fluid is diverted into the upper channel 192.Once the sample is fully injected and the filter material washed,extraction fluid is injected into channel 191. Referring to FIG. 3B, thepressure from the fluid being injected at 191 pushed the moveable flap188 up into a closed position against stencil layer 181. The fluidpasses down through the filter and pushes the nucleic acid off thefilter and into the solution. The sample then passes down 189 to an exitport or another portion of the device for further analysis.

[0036] Another device configuration is shown in FIG. 3C. In thisexample, the stencil layer 182 is composed of a material such that flapregion 188 is normally in the closed position as shown in FIG. 3D. Inuse, the sample is loaded through 192 and passes through the filterregion. The nucleic acid material in this example is stuck on the topsurface of the filter area 190. Once the wash buffer has been passedacross the filter, elution buffer can be added in the reverse direction(see FIG. 3D) and be directed to the exit channel 191. Otherconfigurations are possible, as are other types of sample materials andfilters.

[0037] Another embodiment of the present invention is shown in FIGS.4A-C. In this embodiment, a separate control channel is used to alterthe fluid being pumped. Referring to FIG. 4A, a microfluidic device isshown from the top view with a flow channel 221 and control channel 220.Also shown are a via 227 formed in the sealing layer 224 and a flapregion 226 that form the valve adjacent to central layer 223. Crosssectional views of the valve region are shown in FIGS. 4B and 4C. Inuse, if no pressure is applied to control channel 220, fluid flowsthrough channel 221, reaches the valve region and the pressure of theflow opens the flap valve 226 that covers the via 227. A portion of thefluid then passes into the upper channel 220 as well as the flow channel221. In an alternative use, pressure is applied to the control channel220 during use. If the pressure in control channel 220 is higher thanthe pressure in flow channel 221, the flap 226 completely covers the via227 and all of the fluid flows down channel 221. The pressure in channel220 can be adjusted as desired to produce a pseudo flow regulator in221. If the flap is partially open, then only a smaller portion of fluidwill flow up into 220. In a similar manner, channel 220 could be used asthe flow channel and channel 221 as the control channel. In thisembodiment, all of the fluid would remain in channel 220 and themovement of the flap region 226 would act as a flow constrictor.

[0038] A further embodiment of the present invention is shown in FIGS.5A-C. In this embodiment, the flap 88 is composed in whole or in part ofa material with magnetic susceptibility, such as a ferromagnetic,paramagnetic, or diamagnetic material. The device further includes anmagnetic actuator (not shown), preferably external to the device, fordeforming and therefore controlling the position of the flap 88.Referring to FIG. 5A, a microfluidic device is shown from a side viewwith a no magnetic field is applied to the device, and the flap 88 isshown from side view with an first channel 85 and second and thirdchannels 86, 87 defined between outer layers 80, 84. Inner boundarylayers 81, 83 assist with directing the flow when the flap 88 isdeflected from a substantially linear position aligned with centrallayer 82, such as shown in FIG. 5B. In FIG. 5B, an external magneticforce is applied to the flap 88 in the direction of the dark arrow(upward) using a magnetic actuator (not shown). This upward force causesthe flap 88 to deflect, either just a small amount or sufficiently tocontact the outer layer 84. In the situation where fluid is flowing fromchannel 85 and being split into both channels 86, 87, a small deflectionin the valve may alter the flow characteristics of the liquid in thechannels 86, 87. If sufficient force is applied, the flap 88 may deflectsufficiently to divert all the flow into channel 86. FIG. 5C issubstantially the same as FIG. 5B, but the direction of the magneticforce, represented by the dark arrow, is reversed (downward). In thismanner, a microfluidic device responsive to the application of magneticforce may be constructed to control the flow of liquid.

[0039] The particular devices and construction methods illustrated anddescribed herein are provided by way of example only, and are notintended to limit the scope of the invention. The scope of the inventionshould be restricted only in accordance with the appended claims andtheir equivalents.

What is claimed is:
 1. A microfluidic valve device comprising: a firstmicrofluidic channel disposed in a first layer, the first microfluidicchannel having an upper surface; a second microfluidic channel in asecond layer, wherein the second microfluidic channel has at least onedimension smaller than that of the first channel, the second layerhaving a sealing surface; and a flap layer disposed between the firstmicrofluidic channel and the second microfluidic channel, the flap layerhaving a movable flap formed therein, wherein the flap has a closedposition sealed against the sealing surface and can open into the firstmicrofluidic channel.
 2. The microfluidic device of claim 1, whereinsaid layers are integral.
 3. The microfluidic device of claim 1, whereinsaid layers are stencil layers.
 4. The microfluidic device of claim 3,wherein said stencil layers are polymeric layers.
 5. The microfluidicdevice of claim 3, wherein said stencil layers are adhesive tapes. 6.The microfluidic device of claim 1, wherein the movable flap can contacta second surface of the first layer, wherein such contact restrictsfluid flow within the first channel.
 7. The microfluidic device of claim1, further comprising a fourth layer adjacent to the flap layer.
 8. Themicrofluidic device of claim 7, wherein the fourth layer issubstantially rigid.
 9. The microfluidic device of claim 7, wherein thefourth layer has an aperture disposed therein, wherein the flap can sealagainst the fourth layer adjacent to the aperture.
 10. The microfluidicdevice of claim 1, wherein the flap has a width that is narrower thanthe first channel.
 11. The microfluidic device of claim 1, wherein theflap is flexible.
 12. The microfluidic device of claim 1, wherein theflap is substantially rigid.
 13. The microfluidic device of claim 12,wherein the flap has a hinge region.
 14. The microfluidic device ofclaim 13, wherein the hinge region comprises an area with the flap layerwith reduced thickness relative to the movable portion of the flapregion.
 15. The microfluidic device of claim 13, wherein the hingeregion is formed from a flexible material.
 16. The microfluidic deviceof claim 1, wherein the flap has an upper flap surface and a lower flapsurface and is adhesively coated on either said upper or said lower flapsurface.
 17. The microfluidic device of claim 16, wherein the flap isadhesively coated on both the upper flap surface and the lower flapsurface.
 18. A microfluidic pump comprising: a first microfluidic valveof claim 1; a second microfluidic valve of claim 1; wherein the firstand the second microfluidic valves are in fluid communication with apumping chamber having an adjustable volume.
 19. The microfluidic pumpof claim 18, wherein the pumping chamber comprises a cylinder andmovable piston assembly.
 20. The microfluidic pump of claim 18, furthercomprising a deformable membrane forming one surface of the pumpingchamber.
 21. The microfluidic pump of claim 20, further comprising anactuator for deforming the deformable membrane.
 22. The microfluidicpump of claim 21, wherein the actuator is electromechanical.
 23. Themicrofluidic pump of claim 22, wherein the electromechanical actuator isa piezoelectric or titanium nickel material.
 24. The microfluidic pumpof claim 20, further comprising a pressurizable chamber having at leastone side formed by the deformable membrane.
 25. The microfluidic pump ofclaim 24, further comprising a pressure regulating pump capable ofaltering pressure within the pressurizable chamber.
 26. The microfluidicdevice of claim 1, wherein the flap layer includes a material withmagnetic susceptibility, the device further comprising a magneticactuator.